A zonal mean model of stratospheric tracer transport in isentropic coordinates: Numerical simulations for nitrous oxide and nitric acid
A zonal mean model of stratospheric tracer transport in isentropic coordinates: Numerical simulations for nitrous oxide and nitric acid
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等熵坐标中平流层示踪剂输运的纬向平均模型：一氧化二氮和硝酸的数值模拟
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发表时间：
1985
期刊：
影响因子：
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通讯作者：
N. Sze
中科院分区：
文献类型：
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作者：
M. Ko;K. Tung;D. Weisenstein;N. Sze
利用线性波处理来描述纬向平均模式中的涡旋运动，可以确定不可逆瞬态波是平流层中示踪剂扩散输运的过程。最近基于理想环流模式（GCM）计算和观测到的20°N和80°N之间的瞬态波统计量的估计表明，在平流层中，水平扩散系数应该为≤3×109 cm2 s - 1，比以前大多数二维模式中使用的值小一个数量级。本文建立了平流层微量气体在等熵坐标下纬向平均输送的简单模型，以验证这种小涡扩散假说。在该模型中，假定不可逆瞬态波产生的涡流输运沿等熵面作用，并用单个水平扩散系数Kyy表示。模式中的平流输送受纬向平均非绝热环流的影响，该环流由一个给定的纬向平均非绝热加热速率诊断计算，没有尝试对其进行事后调整。我们表明，观测到的平流层N2O和HNO3的分布可以在模式中充分模拟，Kyy值较小，与上述物理估计一致。平流层痕量气体的观测浓度可以用小的涡流扩散系数值来模拟，这一结果预计同样适用于使用残差平均环流的压力坐标模式。
The use of the linear wave treatment to describe the eddy motions in a zonal mean model leads to the identification of the irreversible transient waves as the process responsible for the diffusive transport of tracers in the stratosphere. Recent estimates based on an idealized general circulation model (GCM) calculation and the observed transient wave statistics between 20°N and 80°N suggest that, in the stratosphere, the horizontal diffusion coefficient should be ≲3×109 cm2 s−1, a value about 1 order of magnitude smaller than values previously used in most two-dimensional models. A simple model of zonally averaged transport of stratospheric trace gases in isentropic coordinates is developed to test this hypothesis of small eddy diffusion. In this model, the eddy transport arising from the irreversible transient waves is assumed to act along the isentropic surfaces and is represented by a single horizontal diffusion coefficient, Kyy. The advective transport in the model is effected by the zonal mean diabatic circulation calculated diagnostically from a given zonal mean diabatic heating rate, of which no post hoc adjustment has been attempted. We show that the observed stratospheric distribution of N2O and HNO3 may be adequately simulated in the model with small values of Kyy that are consistent with physical estimates mentioned above. The result that the observed concentrations of the stratospheric trace gases can be simulated using small values of eddy diffusion coefficients is expected to be equally applicable for models in pressure coordinates using the residual mean circulations.